Flash memory device and operating method for concurrently applying different bias voltages to dummy memory cells and regular memory cells during erasure

ABSTRACT

Integrated circuit flash memory devices, such as NAND flash memory devices, include an array of regular flash memory cells, an array of dummy flash memory cells and an erase controller. The erase controller is configured to concurrently apply a different predetermined bias voltage to the dummy flash memory cells than to the regular flash memory cells during an erase operation of the integrated circuit flash memory device. Related methods are also described.

CLAIM OF PRIORITY

The present application is a continuation of and claims priority fromU.S. patent application Ser. No. 13/047,178, filed Mar. 14, 2011, whichis a divisional of and claims priority from U.S. patent application Ser.No. 11/968,753, filed Jan. 3, 2008, now U.S. Pat. No. 7,924,622, issuedApr. 12, 2011, which claims priority under 35 U.S.C. §119 to KoreanPatent Application No. 10-2007-0081830, filed Aug. 14, 2007, thedisclosures of which are hereby incorporated by reference herein intheir entireties.

FIELD OF THE INVENTION

This invention relates to flash memory devices and operating methodstherefor, and more particularly to erase operations of flash memorydevices.

BACKGROUND OF THE INVENTION

Integrated circuit flash memory devices are widely used nonvolatilememory devices that can be electrically erased in large blocks andreprogrammed. As is well known to those having skill in the art, NOR andNAND flash memory devices may be provided. NOR flash memory devices canprovide random-access read and programming operations, but generally donot offer arbitrary random-access erase operations. NOR flash memorydevices are generally programmed by hot carrier injection. In contrast,NAND flash memory devices generally are accessed for reading and writingby blocks or pages, but can provide relatively low cost and relativelyhigh density. NAND flash memory devices may use Fowler-Nordheim (F-N)tunneling to store data.

A NAND flash memory device is described in U.S. Pat. No. 7,079,437 toHazama et al. entitled “Nonvolatile Semiconductor Memory Device HavingConfiguration of NAND Strings With Dummy Memory Cells Adjacent to SelectTransistors”. As noted in the Abstract of this patent, a nonvolatilesemiconductor memory device having a plurality of electricallyrewritable nonvolatile memory cells connected in series together isdisclosed. A select gate transistor is connected in series to the serialcombination of memory cells. A certain one of the memory cells which islocated adjacent to the select gate transistor is for use as a dummycell. This dummy cell is not used for data storage. During data erasing,the dummy cell is applied with the same bias voltage as that for theother memory cells.

Another NAND-type flash memory cell is described in U.S. PatentPublication 2006/0239077 to Park et al., entitled “NAND Flash MemoryDevice Having Dummy Memory Cells and Methods of Operating Same”. Asnoted in the Abstract of this patent publication, a NAND flash memorydevice includes a control circuit configured to apply, during a programoperation, a first word line voltage to non-selected ones of a pluralityof serially-connected memory cells, a second word line voltage greaterthan the first word line voltage to a selected one of the plurality ofmemory cells, and a third word line voltage lower than the first wordline voltage to a dummy memory cell connected in series with theplurality of memory cells. In other embodiments, a control circuit isconfigured to program a dummy memory cell before and/or after each eraseoperation on a plurality of memory cells connected in series therewith.In still other embodiments, a control circuit is configured to foregoerasure of a dummy memory cell while erasing a plurality of memory cellsconnected in series therewith.

SUMMARY OF THE INVENTION

Integrated circuit flash memory devices according to some embodiments ofthe present invention include an array of regular flash memory cells, anarray of dummy flash memory cells and an erase controller that isconfigured to concurrently apply a different predetermined bias voltageto the dummy flash memory cells than to the regular flash memory cellsduring an erase operation of the integrated circuit flash memory device.As used herein, a “predetermined” bias voltage means that a specificbias voltage is generated and applied to a given flash memory cell,rather than allowing a given flash memory cell to float.

In some embodiments, the different predetermined bias voltage is appliedby applying a read bias voltage, a pass bias voltage, a string selectorline bias voltage, a bit line bias voltage or a predetermined biasvoltage that is less than a floating voltage to the dummy flash memorycells, and concurrently applying a bias voltage that is less than theread bias voltage, the pass bias voltage, the string selector line biasvoltage, the bit line bias voltage or the predetermined bias voltagethat is less than the floating voltage, respectively, to the regularflash memory cells during the erase operation. In other embodiments, theerase controller is configured to concurrently apply a firstpredetermined positive bias voltage, such as 8V, to the dummy flashmemory cells and a second predetermined bias voltage that is less thanthe first predetermined positive bias voltage, such as 0V, to theregular flash memory cells during the erase operation. In still otherembodiments, the erase controller is configured to concurrently apply asecond negative bias voltage, such as −10V, to the regular flash memorycells and a first bias voltage that is less negative than the secondnegative bias voltage, such as 0V, to the dummy flash memory cellsduring the erase operation.

Integrated circuit flash memory devices according to yet otherembodiments of the present invention include an array of regular flashmemory cells, an array of dummy flash memory cells and an erasecontroller that is configured to concurrently apply predetermineddifferent first and second bias voltages to the dummy flash memory cellsand to the regular flash memory cells, respectively, during an eraseoperation of the integrated circuit flash memory device, such that apotential difference between gates of the dummy flash memory cells and awell of the integrated circuit flash memory device is less than apotential difference between the gates of the regular flash memory cellsand the well of the integrated circuit flash memory device during theerase operation. In some specific embodiments, the erase controller isconfigured to apply to the dummy flash memory cells a bias voltagecorresponding to (1) a voltage that is applied to the dummy flash memorycells during a program operation (Vpass), (2) a voltage that is appliedto the dummy flash memory cells during a read operation (Vread), (3) apredetermined voltage that is less than that which is coupled to afloating dummy flash memory cell by the well of the integrated circuitflash memory device (VDL) during the erase operation, (4) a voltage thatis applied to a string selector transistor during a program operation(Vssl), or (5) a voltage that is applied to a bit line under aprogram-inhibit situation during a program operation (Vbl), and toconcurrently apply a predetermined bias voltage that is (1) less thanVpass, (2) less than Vread, (3) less than VDL, (4) less than Vssl, or(5) less than Vbl, respectively, such as of 0V, to the regular flashmemory cells during the erase operation.

In still other embodiments, the erase controller is configured toconcurrently apply a first predetermined positive bias voltage, such as8V, to the dummy flash memory cells and a second predetermined positivebias voltage that is less than the first predetermined positive biasvoltage, such as 0V, to the regular flash memory cells during the eraseoperation, while applying a positive well voltage, such as 20V, to awell of the integrated circuit flash memory device.

In still other embodiments, the erase controller is configured toconcurrently apply a second negative bias voltage, such as −10V, to theregular flash memory cells and a first bias voltage that is lessnegative than the second negative bias voltage, such as 0V, to the dummyflash memory cells during the erase operation, while applying a positivewell voltage, such as 10V, to a well of the integrated circuit flashmemory device.

In some embodiments of the invention, a high voltage generator isprovided that is configured to supply a voltage Vpass that is applied tothe dummy flash memory cells during a program operation, a voltage Vreadthat is applied to the dummy flash memory cells during a read operation,a voltage Vssl that is applied to a string selector transistor during aprogram operation and a voltage Vbl that is applied to a bit line undera program-inhibit situation during a program operation. In theseembodiments, the erase controller may be configured to apply Vpass,Vread, Vssl or Vbl to the dummy flash memory cells during the eraseoperation, and to concurrently apply a bias voltage that is less thanVpass, Vread, Vssl or Vbl, respectively, such as 0V, to the regularflash memory cells during the erase operation.

Other embodiments of the invention provide a high voltage generator thatis configured to supply a voltage Vpass that is applied to the dummyflash memory cells during a program operation, a voltage Vread that isapplied to the dummy flash memory cells during a read operation, avoltage Vssl that is applied to a string selector transistor during aprogram operation, and a voltage Vbl that is applied to a bit line undera program-inhibit situation during a program operation. The high voltagegenerator is further configured to generate a dummy line voltage VDLthat is less than that which is coupled to a floating dummy flash memorycell by a well of the integrated circuit flash memory device, during theerase operation. In these embodiments, the erase controller isconfigured to apply VDL to the dummy flash memory cells during the eraseoperation, and to concurrently apply a bias voltage that is less thanVDL, such as 0V, to the regular flash memory cells during the eraseoperation.

Any and all embodiments of the present invention may be combined with ahost device that is configured to write information into the memorydevice and to read information from the memory device. The host devicemay comprise a memory controller, a microprocessor, a camera, a wirelessterminal, a portable media player, a desktop computer, a notebookcomputer and/or a vehicle navigation system.

Finally, embodiments of the invention have been described above inconnection with an integrated circuit flash memory device, such as aNAND flash memory device, that includes an erase controller configuredas described above. However, analogous methods of erasing an integratedcircuit flash memory device also may be provided according to any andall of the embodiments of the invention that are described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 graphically illustrates deterioration of flash memory cell draincurrent after a large number of erase cycles.

FIG. 2 graphically illustrates threshold voltage shift of flash memorycells after a large number of erase cycles.

FIG. 3 is a schematic diagram of a NAND flash memory device according tovarious embodiments of the present invention.

FIG. 4 is a table that illustrates voltages that may be applied to aNAND flash memory device, such as a NAND flash memory device of FIG. 3,according to various embodiments of the present invention.

FIGS. 5A-5C illustrate alternate embodiments of integrated circuit flashmemory cell arrays of FIG. 3.

FIGS. 6 and 7 are block diagrams of high voltage generators according tovarious embodiments of the present invention.

FIG. 8 is a table of operations that may be performed by controllersand/or methods for erasing integrated circuit flash memory devicesaccording to various embodiments of the present invention.

FIG. 9 is a flowchart of operations that may be performed to erase anintegrated circuit flash memory device according to various embodimentsof the present invention.

FIG. 10 is an overall block diagram of a NAND flash memory device thatincludes a memory cell array according to various embodiments of thepresent invention.

FIG. 11 illustrates a NAND cell array according to various embodimentsof the present invention in combination with a control/decoder circuit.

FIGS. 12-21 illustrate memory devices according to various embodimentsof the present invention in combination with various host devices.

DETAILED DESCRIPTION

The present invention is described more fully hereinafter with referenceto the accompanying drawings, in which embodiments of the invention areshown. This invention may, however, be embodied in many different formsand should not be construed as limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art. In the drawings, the sizes andrelative sizes of layers and regions may be exaggerated for clarity.

It will be understood that when an element is referred to as being“connected to”, “coupled to” or “responsive to” another element (andvariants thereof), it can be directly connected, coupled or responsiveto the other element or intervening elements may be present. Incontrast, when an element is referred to as being “directly connectedto”, “directly coupled to” or “directly responsive to” another element(and variants thereof), there are no intervening elements present. Likereference numerals refer to like elements throughout. As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items and may be abbreviated as “/”.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the present invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” “including” and variants thereof, when used inthis specification, specify the presence of stated features, integers,steps, operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present invention belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

It also will be understood that, as used herein, the terms “row” or“horizontal” and “column” or “vertical” indicate two relativenon-parallel directions that may be orthogonal to one another. However,these terms also are intended to encompass different orientations.

Some embodiments of the present invention may arise from recognitionthat if the same bias voltage is applied to the dummy flash memory cellsas to the regular flash memory cells during an erase operation of anintegrated circuit NAND flash memory device, as described in U.S. Pat.No. 7,079,437, the dummy cells may undesirably experience the same erasestress as a regular memory cell. In particular, as shown in FIG. 1,since the NAND memory architecture connects the regular memory cells andthe dummy memory cells in a serial string, both the regular flash memorycells and the dummy flash memory cells generally exhibit erase stressesshown as ΔId, which signifies the difference in drain current from thetime of production 30 to a time after production after many cycles oferasing 40. The dummy cell current therefore deteriorates by the erasestress ΔId, and the read margin thereby may be decreased.

Moreover, some embodiments of the present invention may also arise fromrecognition allowing the dummy word cells to float during an eraseoperation, as described in U.S. Patent Publication 2006/0239077, alsomay be undesirable. In particular, as illustrated in FIG. 2 at 50, afterproduction, a range of threshold voltages may be exhibited by the dummycells due to variations, for example, in the processing that is used tofabricate the integrated circuit flash memory devices. As also shown at50, the threshold voltage Vth of some cells may be considered abnormal.Moreover, as shown at 60 of FIG. 2, after a large number of programerase cycles, the threshold voltage distribution may shift.Unfortunately, the dummy cells with the higher threshold voltagegenerally will not erase when they are left floating during an eraseoperation due to insufficient voltage being provided between the gateand well of the dummy cell, so as to allow electrons to escape from acharge storage area of the dummy cell. Fewer dummy cells may be erasedover time, which may also degrade the read operation of the NAND memorydevice.

As is well known to those having skill in the art, in NAND flash memorydevices, data erase is performed by applying a voltage between a controlgate and a channel, corresponding to a well region of the flash memorycells, to thereby inject electrons from the channel onto the gate or,alternatively, to draw electrons out of the gate toward the channel.

FIG. 3 is a schematic diagram of a NAND flash memory device that caninclude an erase controller and operational methods according to variousembodiments of the present invention. Referring now to FIG. 3, the NANDmemory device 100 includes a memory cell array 140 that includes aplurality of regular flash memory cells MC and dummy flash memory cellsDMC. Each of the regular memory cells MC and dummy memory cells DMCincludes a floating gate 144 between a control gate 142 and a channel orwell region 146. Each NAND string includes a plurality of regular flashmemory cells MC and one or more dummy flash memory cells DMC seriallyconnected. One or more string selection transistors SST/GST also may beprovided. A regular word line WL or a dummy word line DWL is connectedto the regular flash memory cells MC and dummy flash memory cell(s) DMC,respectively. In FIG. 3, a dummy memory cell DMC is provided at the topand bottom of each string of regular memory cells. However, otherconfigurations also may be provided, as will be described below.

In addition to the memory cell array 140 itself, a plurality of passgates 130, a page buffer 150, a driver 120, a high voltage generator 110and a controller 160 may be provided. As also shown in FIG. 3, the highvoltage generator 110 can generate a word line voltage VWL, a dummy linevoltage VDL and a select line voltage VSL that are applied by the driver120 to the various lines using techniques known to those having skill inthe art. The high voltage generator 110 can also generate erase voltageVers. Controllers 160 and/or high voltage generators 110 according tovarious embodiments of the invention will be described below.

FIG. 4 is a table that illustrates voltages that may be applied to aNAND flash memory device, such as a NAND flash memory device of FIG. 3,according to various embodiments of the present invention. FIG. 4illustrates conventional program, verify and read operations. In theconventional program operation, a program voltage Vpgm is applied to aselected word line, and a pass voltage Vpass is applied to an unselectedword line and a dummy word line. In a verify operation, a verify voltageVvfy is applied to a selected word line, and a read voltage Vread isapplied to an unselected word line and a dummy word line. In a readoperation, 0V is applied to the selected word line, and a read voltageVread is applied to the unselected word line and the dummy word line.

Referring now to the erase operation of FIG. 4, which is also indicatedby “present invention” in FIG. 4, it can be seen that a differentpredetermined bias voltage is applied to the dummy flash memory cellsvia the dummy word line, than to a selected regular flash memory cellvia a selected word line, during the erase operation. As used herein, a“predetermined” bias voltage means that a specific bias voltage isgenerated and applied to a given flash memory cell, rather than allowinga given flash memory cell to float. More specifically, in embodiments ofFIG. 4, 0V is applied to the selected word line, whereas a predeterminedvoltage VDL, Vpass, Vread, Vssl or Vbl is applied to the dummy wordline. These voltages will be described in detail below.

Still referring to the erase column of FIG. 4, a voltage of Vpass,Vread, VDL, Vssl or Vbl is applied to the dummy word line. Vpasscorresponds to a pass bias voltage that is applied to an unselected wordline or a dummy word line during the program operation. Vreadcorresponds to a voltage that is applied to an unselected word line or adummy word line during a read operation. In some embodiments of FIG. 4,the pass voltage Vpass may be 8V and the read voltage Vread may be 6V.VDL is a predetermined bias voltage that is less than that which iscoupled to a floating dummy flash memory cell by the well of theintegrated circuit flash memory device during the erase operation. Vsslcorresponds to a voltage that is applied to a String-Selector Line (SSL)of a string selector transistor during a program operation. Finally, Vblis a voltage that is applied to a bit line under a program-inhibitsituation during a program operation.

More specifically, memory cells are generally erased by a voltagedifference between the word line and the P-well associated therewith. Anerase voltage Vers, for example 20V, may be applied to the P-well inoperations of FIG. 4, Dummy cells are soft erased by the voltagedifference between the dummy word line and the P-well. Accordingly, VDLis set to be a predetermined bias voltage that is more than 0V but lessthan the dummy line voltage coupled by Vers in the case of a floatingdummy cell. The abnormal dummy cells are reset by the soft erase, sothat the error of the read operation may be reduced. In some embodimentsof FIG. 4, about 18V may be coupled to a floating dummy flash memorycell by the well of the integrated circuit flash memory device, so thatVDL may be a predetermined bias voltage of about 16V or about 17V thatis generated and applied in some embodiments of the present invention.

Accordingly, erase operations of the present invention may provide apotential difference between the gates of the dummy flash memory cellsand the well of the integrated circuit flash memory device that is lessthan a potential difference between control gates of the regular flashmemory cells and the well of the integrated flash memory device duringthe erase operation.

Generalizing from the embodiments of FIG. 4, integrated circuit flashmemory devices according to some embodiments of the present inventionconfigure an erase controller to apply to the dummy flash memory cells afirst predetermined bias voltage corresponding (1) a voltage that isapplied to the dummy flash memory cells during a program operation(Vpass), (2) a voltage that is applied to the dummy flash memory cellsduring a read operation (Vread), (3) a predetermined voltage that isless than that which is coupled to a floating dummy flash memory cell bythe well of the integrated circuit flash memory device (VDL) during theerase operation, (4) a voltage that is applied to a string selectortransistor during a program operation (Vssl), or (5) a voltage that isapplied to a bit line under a program-inhibit situation during a programoperation (Vbl), and to concurrently apply a bias voltage that is (1)less than Vpass, (2) less than Vread, (3) less than VDL, (4) less thanVssl or (5) less than Vbl, respectively, such as 0V, to the regularflash memory cells during the erase operation.

FIGS. 5A-5C illustrate alternate embodiments of integrated circuit flashmemory cell arrays 140 of FIG. 3. Recall that in FIG. 3, a single dummymemory cell is used at the top and the bottom of each string of regularmemory cells MC. In contrast, in FIG. 5A, two dummy memory cells areused at the top and bottom of each string of regular memory cells. Inembodiments of FIG. 5B, a single dummy cell is used at the top and apair of dummy cells is used at the bottom of each NAND string, whereasin FIG. 5C, two dummy cells are used at the top and a single dummy cellis used at the bottom of a given NAND string. Various otherconfigurations of dummy cells and regular cells may be used in variousembodiments of the present invention, and need not be described furtherherein.

Referring back to FIGS. 3 and 4, as was already described, someembodiments of the present invention provide the pass voltage Vpass orthe read voltage Vread to the dummy word lines during the eraseoperation. In these embodiments, an existing high voltage generator 110may be used and a driver 120 and/or controller 160 may be modified toalso provide the read voltage Vread or pass voltage Vpass to the dummyword lines during the erase operation. Accordingly, as shown in FIG. 6,a high voltage generator 110′ may include a word line voltage generator115 that applies the word line voltages VWL and also generates the passvoltage Vpass or read voltage Vread. The string selector line biasvoltage and the bit line bias voltage also may be generated. An erasevoltage generator 116 and a select line voltage generator 117 may alsobe provided. Thus, the bias voltages Vread or Vpass may be applied tothe dummy word lines and an additional dummy line voltage generator neednot be provided. The high voltage generator 110′ generates eraseoperation voltages in response to a mode signal ERS, which istransferred from the controller 160 and signifies an erase mode.

In contrast, when a dummy word line voltage VDL is generated that isless than that which is coupled to a floating dummy flash memory cell bythe well of the integrated circuit flash memory device, a separategenerator for this predetermined bias voltage VDL may need to beprovided. Thus, as shown in FIG. 7, a conventional word line voltagegenerator 111, an erase voltage generator 113 and select line voltagegenerator 114 may be provided. However, a VDL generator 112 also may beprovided that generates the dummy line voltage VDL, as was describedabove. The high voltage generator 110″ generates erase operationvoltages in response to a mode signal ERS, which is transferred from thecontroller 160 and signifies an erase operation. Accordingly, a separateVDL generator 112 may be provided in a high voltage generator 110″ togenerate the VDL voltage, which is then applied to the dummy cellsduring, erase.

FIG. 8 summarizes controllers and methods for erasing integrated circuitflash memory devices according to various embodiments of the presentinvention. Embodiment 3 corresponds to the second column of FIG. 4 thatwas identified by “present invention”, in that the SSL and GSL arefloating (signified by F), the P-well or bulk is provided with an erasevoltage Vwell, the selected word line is biased at 0V, and the dummyword lines are biased at Vread, Vpass, VDL, Vssl or Vbl. Thus,Embodiment 3 illustrates embodiments of the present invention whereinthe erase controller is configured to apply to the dummy flash memorycells a first predetermined bias voltage corresponding to (1) Vpass, (2)Vread, (3) VDL (4) Vssl or (5) Vbl during the erase operation, toconcurrently apply the bias voltage that is (1) less than Vpass, (2)less than Vread, (3) less than VDL, (4) less than Vssl or (5) less thanVbl, respectively, such as 0V, to the regular flash memory cells duringthe erase operation.

In contrast, in Embodiment 1, the dummy line is biased at 8V, theselected word line is biased at 0V and the bulk or well is biased at20V. Accordingly, Embodiment 1 illustrates embodiments of the presentinvention wherein the erase controller is configured to concurrentlyapply a first predetermined positive bias voltage, such as 8V, to thedummy flash memory cells, and the second predetermined positive biasvoltage that is less than the first predetermined bias voltage, such as0V, to the regular flash memory cells during the erase operation, whileapplying a positive well voltage, such as 20V, to a well of theintegrated circuit flash memory device.

Moreover, in Embodiment 2, the dummy cells are biased at 0V, theselected word line is biased at −10V and the bulk or well is biased at10V during the erase operation. Accordingly, Embodiment 2 illustratesembodiments of the present invention wherein the erase controller isconfigured to concurrently apply a second negative bias voltage, such as−10V, to the regular flash memory cells, and a first bias voltage, suchas 0V, that is less negative than the second negative bias voltage, tothe regular flash memory cells during the erase operation, whileapplying a positive well voltage, such as 10V, to a well of theintegrated circuit flash memory device.

In each of the cases illustrated in FIG. 8, the potential differencebetween the regular word line and the well is greater than the potentialdifference between the dummy word line and the well during erase. Moreparticularly, in Embodiment 3, the difference between the regular cellvoltage and the well voltage is Vwell minus 0V or Vwell, whereas thedifference between the dummy word line and the well is Vwell minus Vreador Vpass or VDL, so that the potential difference between the regularcell and the well is greater than the potential difference between thedummy cell and the well during erase. Similarly, in Embodiment 2, thepotential difference between the regular cell and the well is 10V minus−10V or 20V, whereas the potential difference between the dummy cell andthe well is 10V minus 0V or 10V. Finally, in Embodiment 1, thedifference between the regular cell and the well is 20V minus 0V or 20V,and the difference between the dummy and the well is 20V minus 8V or12V. Thus, in all of these embodiments, the potential difference betweenthe regular cell and the well is greater than the potential differencebetween the dummy cell and the well during erase. Stated differently,first and second predetermined bias voltages are applied to the dummyflash memory cells and to the regular flash memory cells, respectively,such that a potential difference between the gates of the dummy flashmemory cells and a well of the integrated circuit flash memory device isless than a potential difference between the gates of the regular flashmemory cells and the well of the integrated circuit flash memory deviceduring the erase operation.

FIG. 9 is a flowchart of operations that may be performed to erase anintegrated circuit flash memory device according to various embodimentsof the present invention. These embodiments may be performed by the highvoltage generators 110, 110′, 110″ in conjunction with the controller160 and driver 120 of FIG. 3. Specifically, referring to FIG. 9, theerase voltage Vers, the word line voltage VWL, the dummy line voltageVDL and the select line voltage VSL are generated at Block 910. As wasalready explained, rather than a predetermined dummy line bias voltageVDL, the pass voltage Vpass, the read voltage Vread, the string selectorline bias voltage Vssl or the bit line bias voltage Vbl may besubstituted. Then, at Block 920, the generated voltages are supplied tothe cell array by providing VDL, Vpass, Vread, Vssl or Vbl to the dummyword line, and providing the other voltages as shown. An erase verifyoperation is then performed at Block 930, and if the erase verifyoperation is successful, then the erase ends. If not, operations ofBlock 910, 920 and 930 are again performed. FIG. 10 is an overall blockdiagram of a NAND flash memory device that includes a memory cell array310 according to any of the herein described embodiments of the presentinvention. Page buffers 320 and a Y-gating circuit 330 are provided, aswell as a control/decoder circuitry 340 that is responsive to commandsCMD and addresses ADDRESS. FIG. 11 illustrates a NAND cell array 310 andthe control/decoder circuit 340 of FIG. 10.

Memory devices according to various embodiments of the present inventionmay be employed in combination with a host device that is configured towrite information into the memory devices and to read information fromthe memory devices. Thus, for example, FIG. 12 illustrates a memory card530 that includes a memory controller 520 and a memory 510 according toany embodiments of the present invention. FIG. 13 illustrates the use ofa memory card 530 in a digital camera 55. FIG. 14 illustrates the use ofa memory card 530 in a wireless terminal, such as a mobile phone 500.FIG. 15 illustrates a memory device 510 according to any embodiments ofthe present invention in combination with a portable media player 600,such as an MP3 player or other portable player device, and can include amemory controller 520, a device controller 610, an interface 630 andpresentation components 620. FIG. 16 illustrates a memory 510 incombination with a general host 700 and FIG. 17 illustrates integrationof the memory 510 and a memory controller 520 onto a card 530 and usedwith a host 700, which can be a personal computer. FIG. 18 illustrates acard 800 that includes a CPU 810 and a memory 510 and that may beincluded in a notebook computer 800 shown in FIG. 19. The card 800 maybe used instead of, or in addition to, hard disk drives. FIG. 20includes a vehicle 800 that includes a microprocessor 800 having a CPU810 and memory 510 according to any embodiments of the present inventionand that may be used as part of a vehicle navigation system. Finally,FIG. 21 illustrates a memory card 530 including memory 510 according toany embodiments of the present invention and a memory controller 520that can be used as part of an airplane navigation system.

In the drawings and specification, there have been disclosed embodimentsof the invention and, although specific terms are employed, they areused in a generic and descriptive sense only and not for purposes oflimitation, the scope of the invention being set forth in the followingclaims.

What is claimed is:
 1. An integrated circuit flash memory devicecomprising: an array of regular flash memory cells; an array of dummyflash memory cells; and an erase controller that is configured to setthe dummy flash memory cells to a different predetermined bias voltagefrom the regular flash memory cells during an erase operation of theintegrated circuit flash memory device, wherein the erase controller isconfigured to set the dummy flash memory cells to a predetermined biasvoltage that is less than a floating voltage and to apply a bias voltagethat is less than the predetermined bias voltage that is less than thefloating voltage to the regular flash memory cells during the eraseoperation, and wherein the dummy flash memory cells and the regularflash memory cells are serially connected to provide a NAND flash memorydevice.
 2. An integrated circuit flash memory device according to claim1 wherein the erase controller is configured to set the dummy flashmemory cells to a first predetermined positive bias voltage and to setthe regular flash memory cells to a second predetermined positive biasvoltage that is less than the first predetermined positive bias voltageduring the erase operation.
 3. An integrated circuit flash memory deviceaccording to claim 1 wherein the erase controller is configured to setthe regular flash memory cells to a second negative bias voltage and toset the dummy flash memory cells to a first negative bias voltage thatis less negative than the second negative bias voltage during the eraseoperation.
 4. A method of erasing an integrated circuit flash memorydevice that includes an array of regular flash memory cells and an arrayof dummy flash memory cells, the method comprising: setting the dummyflash memory cells to a different predetermined bias voltage from theregular flash memory cells during an erase operation of the integratedcircuit flash memory device, wherein setting the dummy flash memorycells to a different predetermined bias voltage comprises setting thedummy flash memory cells to a predetermined bias voltage that is lessthan a floating voltage and applying a bias voltage that is less thanthe predetermined bias voltage that is less than the floating voltage tothe regular flash memory cells during the erase operation, and whereinthe dummy flash memory cells and the regular flash memory cells areserially connected to provide a NAND flash memory device.
 5. A methodaccording to claim 4 wherein setting the dummy flash memory cells to adifferent predetermined bias voltage comprises setting the dummy flashmemory cells to a first predetermined positive bias voltage and settingthe regular flash memory cells to a second predetermined positive biasvoltage that is less than the first predetermined positive bias voltageduring the erase operation.
 6. A method according to claim 4 whereinsetting the dummy flash memory cells to a different predetermined biasvoltage comprises applying a second negative bias voltage to the regularflash memory cells and a first negative bias voltage that is lessnegative than the second negative bias voltage to the dummy flash memorycells during the erase operation.